The invention relates to a data transmission method in a communication network, especially cellular radio network, in which data, especially data packets of a packet-oriented data service, are transmitted over a data channel jointly used by several terminals and several jointly used control channels are used for signaling the specific mobile station(s) for which the data is intended.
In UMTS (Universal Mobile Telecommunication System) data packets are sent to User Equipment (UE) over the High-Speed Downlink Shared Channel (HS_DSCH). The associated control information is transmitted in parallel over the High-Speed Shared Control Channel (HS_SCCH). A maximum of four of these HS_SCCHs are assigned to a mobile station. So that the receiving mobile station can recognize that the information on the HS_SCCH and the data on the HS_DSCH is intended for it, the control information is linked to identification information specific to a mobile station. For a more precise definition of terms the reader is referred to the description of the Figures below.
In UMTS the HS_DSCH is shifted in relation to the HS_SCCH by two time slots and three time slots of both the HS_SCCH and of the HS_DSCH correspond to one information unit of the physical layer (the length of an information unit is referred to as a subframe).
As well as the mobile station-specific identification information a unit of the HS_SCCH also contains information about                the HS_DSCH spreading codes or channelization codes used,        the modulation scheme, for example QPSK (Quadrature Phase Shift Keying) or 16 QAM (16 Quadrature Amplitude Modulation),        the number of the data bits which are transferred from the physical layer to the next higher layer,        the indication as to whether this is a first data transmission or a retransmission of the data,        the HARQ process number,        the information relating to the mapping specification of the data bits to the 16 QAM modulation used and regarding the rate adaptation pattern.        
The information relates in each case to the HS_DSCH information unit transmitted 2 time slots later.
In UMTS a mobile station must monitor up to four HS_SCCHs if it has not already received data intended for it in the immediately preceding HS_SCCH unit. An example with 4 HS_SCCHs is selected below, but a different number is similarly possible, such as 2 or 3. Conversely, in the UMTS standard it is true to say that a mobile station which receives the control information intended for it on one of the HS_SCCHs, in the subsequent interval of the length of three time slots only monitors one HS_SCCH, this being the HS_SCCH on which the control information was previously received. The reason for this is that it allows parts of the receiver hardware which will be needed for HS_SCCH receiving, in the event of data transmission on the HS_DSCH, to be able to be used for HS_DSCH receiving and thereby fewer resources are needed overall. This is referred to as the consecutive scheduling rule.
Furthermore different categories of mobile stations, i.e. mobile stations with different service features, are used in UMTS. As regards packet-oriented high-speed data transmission a mobile station is identified in accordance with its category, especially in the following capabilities                the maximum number of HS_DSCH channelization codes which it can simultaneously receive and process in an HS_DSCH unit,        the minimum period of time between two consecutive data transmissions on the HS_DSCH which it can process,        the modulation scheme (QPSK, 16 QAM) which it can process,and further parameters.        
In addition the physical layer is informed via signaling by higher layers of the OSI (Open system Interconnection) models about the number of Hybrid Automatic Repeat Request (HARQ) process and the maximum transport block size or packet size.
An example of inconsistent information in the case of UMTS is if the number of HS_DSCH channelization codes used transmitted in the HS_SCCH unit is greater than the maximum number of HS_DSCH channelization codes which the mobile station must be able to process in accordance with its category or/and if the number of the HARQ process is higher than the number of HARQ processes configured for this mobile station.
If a mobile station establishes that the information in an HS_SCCH unit which it evaluates in accordance with its identification as intended for it does not contain consistent information, the physical layer can in this case reject the information and not forward it. The advantage of this method is that the likelihood of a transfer of erroneous packets from the physical layer to higher layers is reduced by those packets which appear to contain inconsistent information being filtered out. Since the inconsistent control information itself is not passed on to higher layers since it is only needed in the physical layer, such filtering can only be performed in the physical layer. Inconsistent data can under some circumstances lead to serious malfunctions at higher layers, thus great importance has been placed in the UMTS specification on avoiding such errors as far as possible. In addition to further methods such as checksum tests, the consistency checking described is a method for avoiding such erroneous behavior.
It can now be the case that data which could actually have been correctly received is also rejected by such consistency checking: For example it can be the case that a mobile station is requested to used 5 HS_DSCH spreading codes or channelization codes which corresponds to its maximum capability. Errors in transmission can now mean that the mobile station incorrectly believes that it has to receive 15 codes. If, instead of this, it now receives the maximum possible number of codes, namely 5, it would have corrected the incorrect transmission of the control information using this method. The mobile station should not attempt however to correct errors in control information but instead should detect errors and reject the entire data frame.
The disadvantage of this is that data can be rejected incorrectly.